An IR remote control, as a remote control device transmitting control signals by IR signals with a wavelength from 0.76 μm to 1.5 μm, is widely used in the field of industrial control and household electrical appliances. The IR signal is converted from an electrical signal, e.g., the high/low level of the electrical signal is indicated by presence/absence of the IR light, respectively. And the electrical signal (i.e., the control signal) is a modulated signal formed by modulation of an IR control code onto a carrier.
The IR control code is used for representing a remote control instruction. As shown in FIG. 1, with the remote control instruction as a string of binary digits, the IR control code represents the remote control instruction by the combination of high and low levels. Taking the NEC protocol format definition for an example: In the IR control code, a binary digit 0 is represented by the combination of a high level for a duration of 0.5625 ms and a low level for a duration of 0.5625 ms, and a binary digit 1 is represented by the combination of a high level for a duration of 0.5625 ms and a low level for a duration of 1.6875 ms. The carrier signal is a square wave signal. The control signal is a modulated signal formed by modulation of the IR control code onto a carrier through pulse amplitude modulation (PAM). The pulse amplitude modulation means that the high and low levels of the IR control code are indicated by the carrier square wave signal and the low level in the modulated signal, respectively.
A self-learning remote control is a universal IR remote control that, after learning the original remote control, has the IR remote control function of the original remote control. Colloquially, the self-learning remote control is equivalent to a key blank that can copy any shape of keys.
The self-learning remote control is divided into two categories, a fixed code format self-learning remote control and a waveform copy self-learning remote control.
The fixed code format self-learning IR remote control is achieved by first collecting, summarizing and classifying the IR remote control signals used on the market, and then preparing a decoding program and an emitting program for each category. Its learning process is as follows: Determining the category of the existing IR remote control signal, selecting the decoding program and emitting program of the IR remote control signal of this category, and storing the programs in a memory such as EEPROM. The fixed code format self-learning IR remote control is advantageous in having low requirements for operating frequency of the master chip and capacity of the memory, but disadvantageous in only learning the IR remote control signals that have been collected. A typical representative of this self-learning remote control is the New HTC One cell phone of the HTC company.
The waveform copy self-learning IR remote control is achieved by copying completely an IR remote control signal emitted by the original remote control regardless of the format, and compressing the IR remote control signal before storing it in the memory. In need of emission, the compressed IR remote control signal is read by the memory, and extracted to the original IR remote control signal before being emitted. The waveform copy self-learning IR remote control is advantageous in the ability of learning any type of IR remote control signals, but disadvantageous in having high requirements for operating frequency of the master chip and capacity of the memory. A typical representative of this self-learning remote control is a cell phone OTG self-learning remote control accessory of Tianjia (Shanghai) Information Technology Co., Ltd.
The existing waveform copy self-learning IR remote control usually uses an integrated IR receiver, and has two drawbacks:    1) The integrated IR receiver can only receive an IR signal, but cannot emit an IR signal.    2) With the IR signal modulated by a carrier, the integrated IR receiver directly filters out the carrier. This makes the waveform copy self-learning IR remote control using the integrated IR receiver has to supplementarily record the carrier information by an auxiliary means after learning.